Going off of what @Sebastian-Roth said, you could shrink the disk before imaging, and when v0.10.0 of the client is released, create a snapin to auto expand the disk. That way as soon as osx boots up after imaging, the client pulls the auto-expand snapin and runs it.

@PioDer AFAIK there is no open source tool to resize HFP+ filesystems (like resize2fs that we use to resize EXT filesystems). I don’t think we will be able to port OS X diskutil to linux any time soon. Please let us know if you know other tools that can resize HFS+!

Are you able to image your OS X clients with non-resizable images? Why do you need resizable? You could just image as non-resizable and expand using diskutil in Mac OS X after cloning…